Allergic rhinitis involves inflammation of nasal mucous membranes in sensitised individuals when inhaled allergenic particles contact mucous membranes and elicit a response mediated by immunoglobulin E (IgE). There are two types: seasonal and persistent (formerly called “perennial”) allergic rhinitis.
WHAT ARE THE CAUSES OF ALLERGIC RHINITIS?
Airborne allergens enter the nose during inhalation and are processed by lymphocytes, which produce antigen-specific IgE, sensitising genetically predisposed hosts to those agents. On nasal reexposure, IgE bound to mast cells interacts with airborne allergens, triggering the release of inflammatory mediators.
An immediate reaction occurs within seconds to minutes, resulting in rapid release of preformed and newly generated mediators from the arachidonic acid cascade. Mediators of immediate hypersensitivity include histamine, leukotrienes, prostaglandin, tryptase, and kinins. These mediators cause vasodilation, increased vascular permeability, and production of nasal secretions. Histamine produces rhinorrhea, itching, sneezing, and nasal obstruction.
A late-phase reaction may occur 4 to 8 hours after initial allergen exposure due to cytokine release from mast cells and thymus-derived helper lymphocytes. This inflammatory response causes persistent chronic symptoms, including nasal congestion.
WHAT ARE THE SIGNS AND SYMPTOMS OF ALLERGIC RHINITIS?
Seasonal (hay fever) allergic rhinitis occurs in response to specific allergens (pollen from trees, grasses, and weeds) present at predictable times of the year (spring and/or fall) and typically causes more acute symptoms.
Persistent allergic rhinitis occurs year-round in response to nonseasonal
allergens (e.g., dust mites, animal dander, and moulds) and usually causes more subtle, chronic symptoms.
Many patients have a combination of both types, with symptoms year-round and seasonal exacerbations.
Symptoms include clear rhinorrhea, sneezing, nasal congestion, postnasal drip, allergic conjunctivitis, and pruritic eyes, ears, or nose.
In children, a physical examination may reveal dark circles under the eyes (allergic shiners), a transverse nasal crease caused by repeated rubbing of the nose, adenoidal breathing, edematous nasal turbinates coated with clear secretions, tearing, and periorbital swelling.
Patients may complain of loss of smell or taste, with sinusitis or polyps the underlying cause in many cases. Postnasal drip with cough or hoarseness can be bothersome.
Untreated rhinitis symptoms may lead to insomnia, malaise, fatigue, and poor work or school performance.
Allergic rhinitis is associated with asthma; 10% to 40% of allergic rhinitis patients have asthma.
Complications include recurrent and chronic sinusitis and epistaxis.
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